Bowls are often small and they are difficult to fit heaters and filters into. Their rounded shape also distorts the view of your beautiful betta.
Small bowls are not ideal because in such small spaces, bettas develop neurotic behaviors such as tail biting and glass surfing and often become obese from lack of exercise. They also often die from ammonia building up too quickly in such a small space.
Fish constantly excrete ammonia through their gills--kind of like urine. In order to keep the ammonia level down in a 1 or 1.5 gallon bowl, you would need to change 100% of the water and clean out the bowl with hot water every 3-4 days. That's a lot of work. In a larger, filtered tank, the tank undergoes a process called the Nitrogen cycle. The filter is colonized by special bacteria that break down the poisonos ammonia into poisonous nitrite, then more bacteria break it down into nitrate. Nitrates can be tolerated in much higher amounts than the other two compounds--so instead of doing those 100% water changes every few days, you only do 1 partial water change per week. Sounds a lot better, right?
Besides, bettas need stable temperatures of 78-83 to be comfortable, healthy and active. In lower temps, their circulation and digestion can be negatively affected, causing your fish to have digestive problems and be more vulnerable to illness. It is difficult to fit an appropriate heater into a bowl--the best heaters are ones with a thermostat and a dial that you can adjust the temperature with. Other heaters such as pads and pre-sets are not ideal.
Caring for your fish in a tank is easier, and it's easier to appreciate your fish through the flat sides of a normal fish tank.
There are a lot of opinions on the minimum tank size for bettas, personally, I would say that the minimum is at least 2.5 gallons--simply because of the fact that most heaters were designed to work in tanks that are 2.5G or larger. The bigger the aquarium, the less maintenance you will have to do, the happier your fish will be, and generally the bigger the aquarium, the cheaper they are per gallon.
Actually, at one time I kept a betta in a 2 gal. glass drum bowl. The flat sides of the drum bowl allowed me to add a small internal filter & a small heater behind a piece of driftwood. Had a little gravel in there, some java moss attached to the driftwood & and a moss ball. Did twice a week cleanings & everything went fine.
I decided, however, to upgrade him to a tank because I wanted to give him more room & wanted something with a top and a light on it.
Depends on the size of the bowl. Like above ^ 2g drum bowls work GREAT! I have one for my boy who doesn't like divided tanks and water currents. He has a little theo heater and everything works out great. Twice weekly water changes and he's happy as a clam.
IMO anything under 2g is not suitable. (although there are exceptions. I have a boy who has bad bloating and very very long pectoral fins making it hard for him to swim, so he is in a 1g, but other then for medical reasons, I don't recommend it.)
I have mine in a .5 gal bowl with no filter or heater...is that okay for now or should i run to the store and upgrade right away?!?
Run to store!!!! :) (Resist buying more bettas while you're there)
hmm..maybe I need to run to the store as well..I feel like I go to often and everyone's like "It's the betta girl again, the one that holds up each cup and separates them so they don't flare" Lol!
I LOVE critter keepers BTW-they are awesome and have lids, easy to clean and cheep!
I just bought a 5 gallon for Clampy-he looooves it, I also have a 3 gallon which I recommend as the minimum size for betta keeping, I have smaller 1.5 gallons but they are temporary for quarantining new fish.